1. Field
This application relates generally to wireless communication and more specifically, but not exclusively, to the routing of packets during a communication handoff.
2. Introduction
The mobile Internet Protocol (“IP”) standard promulgated by the Internet Engineering Task Force describes a scheme that enables a mobile node to send and receive packets as it moves within a wireless network. In this scheme, a home (e.g., permanent) IP address may be assigned to the mobile node whereby any other device that wishes to send packets to the mobile node sends the packets to this home IP address. In the event the mobile node is connected to a sub-network other than its home sub-network (i.e., the sub-network associated with the home IP address), packets sent to the home IP address are forwarded to the mobile node at the other sub-network. In this way, the mobile node may receive any packets sent to the home IP address regardless of the current location of the mobile node.
In mobile IP, forwarding of packets in this manner is achieved through the use of mobility agents. For example, when the mobile node establishes communication with a network access node (e.g., a base station) of a sub-network other than its home sub-network, the mobile node registers with a routing node on that sub-network. This routing node may serve as a foreign agent for the mobile node that provides a care of address (“CoA”) to which packets destined for the mobile node may be routed. In a typical case, the CoA associated with a foreign agent is the IP address of that foreign agent.
A routing node that is connected to the mobile node's home sub-network is designated as the mobile node's home agent. The home agent intercepts packets sent to the home IP address and forwards the packets via an IP tunnel to the CoA associated with the foreign agent. The foreign agent routes the packets it receives from the IP tunnel to the network access node which then sends the packets to the mobile node.
The foreign agent may route any packets it receives from the mobile node to the designated destination via normal IP routing or it may send them to the home agent. In the latter case, the foreign agent will use the IP tunnel to forward the packets the home agent.
The mobile node may connect to different network access nodes as it roams through the network. Some of these network access nodes may be associated with different foreign agents that are, in turn, associated with different CoAs. Consequently, as the mobile node performs a handoff from one network access node to another, the IP tunnel from the home agent may need to be reestablished each time the mobile node registers with a new foreign agent.
In some cases, a session may be active at the mobile node when it performs a handoff from one network access node to another. In such cases, packets sent to a CoA associated with a given network access node may not reach the mobile node after the mobile node establishes communication with a new network access node that is associated with a new CoA. Accordingly, there is a need to mitigate packet loss during communication handoffs.